Simple Recipes for Real Science

Tag: filters’

I demonstrated this experiment on Kare11. Click here to watch the clip.Don’t drink the water you purify when you do this experiment at home, since it may still contain harmful microbes!!! You can use homemade Petri dishes to see how clean you got your water though, by swabbing the unfiltered water on one dish and the water you purified on another to see what grows!

If you’re in a survival situation, it’s important to do everything you can to make sure the water is safe, before you drink it! The first thing you have to do is make the water you find clear enough to read a paper through (get out the gunk, in other words.) Then, you have to put it in the sun for six hours so ultraviolet rays will kill anything living in the water. Digging a hole next to a pond and collecting the water that seeps in will pre-filter the water for you! Using grass, charcoal, sandy soil, you can make a water filter. A plastic water bottle with the bottom cut off works best as a filter-holder, but you can use a cone made of birch bark if you don’t have a bottle!

We cut the bottoms off of some water bottles, pounded up some charcoal (you could use campfire coals for the charcoal layer!), pulled some grass and found some sand (don’t use sand from a sandbox, which may contain cat feces.)

Next, we layered grass, charcoal and sand in our bottles, packing each layer down as much as possible. I tried grass, charcoal, sand, charcoal and more grass, but the girls made more layers than I did. We wrote down what we did to see who got the cleanest water!
Then, we poured stream water through our filters and collected what flowed through in empty sports drink bottles. We covered the bottles and left them in the sun for at least six hours. Last night, we stuck cotton swabs in each water sample and swabbed homemade petri dishes to test the water for fungi and bacterial growth. (You can’t see viruses, but the sun will often kill them efficiently.) Our controls were stream water that was unfiltered and keep out of the sun and stream water that was unfiltered, but put in the sun with the other samples. Note: If you want to make petri dishes to test your water, use agar instead of gelatin to make the plates! Some bacteria are good at breaking down gelatin, turning it into a liquid, and this happened to a few of our samples (including the unfiltered water.)
We observed that putting the water through our filters made it yellow and one sample was a little cloudy, so it will be interesting to see how it compares to the stream water we didn’t filter or put in the sun. It would be fun to test the filter ingredients to see what made it yellow.